add option to control the background color of the exported image (#576)

src/plugins/jsmind.screenshot.js

@@ -25,6 +25,7 @@ const DEFAULT_OPTIONS = {
  left: $.w.location,
  right: 'https://github.com/hizzgdev/jsmind',
  },
+ background: 'transparent',
 };
 
 class JmScreenshot {
@@ -42,6 +43,7 @@ class JmScreenshot {
  let c = this.create_canvas();
  let ctx = c.getContext('2d');
  Promise.resolve(ctx)
+ .then(() => this.draw_background(ctx))
  .then(() => this.draw_lines(ctx))
  .then(() => this.draw_nodes(ctx))
  .then(() => this.draw_watermark(c, ctx))
@@ -62,6 +64,19 @@ class JmScreenshot {
  c.parentNode.removeChild(c);
  }
 
+ draw_background(ctx) {
+ return new Promise(
+ function (resolve, _) {
+ const bg = this.options.background;
+ if (!!bg && bg !== 'transparent') {
+ ctx.fillStyle = this.options.background;
+ ctx.fillRect(0, 0, this.jm.view.size.w, this.jm.view.size.h);
+ }
+ resolve(ctx);
+ }.bind(this)
+ );
+ }
+
  draw_lines(ctx) {
  return new Promise(
  function (resolve, _) {